EAGER: Magnetic Nanostructures with Perpendicular Anisotropy

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Non-Technical AbstractA key attribute of a magnetic material is the ability to retain its magnetic moment in certain directions, or magnetic anisotropy. For example, an iron needle is usually magnetized along its long axis and a thin iron foil would have its moments lying in the film plane. Certain nanoscale magnets in thin film forms, however, prefer to orient their moments perpendicular to the films - known as perpendicular magnetic anisotropy. Such nanomagnets are technologically important, as they allow much more efficient information storage at higher densities, analogous to the benefits of building skyscrapers with small real-estate footprints. This project investigates two types of such nanomaterials that have potentially transformative technological impacts: 1. ordered alloys of iron/platinum-based materials as storage media in next generation ultrahigh density magnetic recording; 2. a novel type of nanomagnet arrays where the magnetic moments take up a special arrangement known as the skyrmion state. The magnetic skyrmions offer potentially new mechanisms for information storage that is not only robust, but also highly energy efficient, expected to be at a tiny fraction of the energy cost of current technologies. Students involved will receive exposure to research experiences in university, national laboratory and user-facility, and industrial research and development. Technical AbstractAlloys of FePt-based materials in the ordered phase are promising media choices for the emerging heat-assisted magnetic recording technology due to their high anisotropy, large saturation magnetization, and moderate Curie temperature. This project addresses critical challenges in the convenient realization of the high anisotropy phase, and understanding and control over the switching field distribution. Thin films of FePt-based alloys in the ordered phase are investigated. Basic understanding and control of the magnetization reversal are gained through magnetometry and first-order reversal curve studies at elevated temperatures. The second research area focuses on magnetic skyrmions that exhibit topologically protected quantum states and other unique topological phenomena. Hybrid skyrmion lattices based on perpendicular anisotropy films are synthesized and investigated to demonstrate the ground state at room temperature. A set of magnetic field sequences is followed to establish the skyrmion lattices, as well as vortex lattices and mixed lattices for comparison. Magnetic imaging, polarized neutron reflectometry, magneto-transport studies, and micromagnetic simulations are carried out to probe the skyrmions and their responses to external stimuli. These artificial skyrmions are expected to be stable over wide temperature and field ranges, thus offering an exciting platform to explore the intriguing physics in such exotic spin textures.